Having completed the game, I`d say get lots of demons and don`t be afraid to fuse them. Don`t be surprised if you spend a lot of time fusing them. Get extras of the same demons for fusing too.

For me, I try to have demons with a large variety of moves, like different elemental spells. The more spells you have, the more opportunities you have to exploit the weaknesses of your opponents and gain a lot of extra turns.

Try to get rid of as many of your demons` weaknesses as you can. The more you have, the more often the enemies can turn the tables on you and destroy your team. I`ve had fights where the enemies completely murder me due to exploiting my weaknesses.

Hmm, that`s about all I`ve got. Hope this helps, and I hope you enjoy the game. It can be frustrating, but I really enjoyed it.

How do you do that? Like fuse with a demon's who's resistanced and weaknesses cancel out?

I had no experience until a year ago when I played Persona 3 Portable on PSP - at first I liked it but I needed to take two breaks that lasted for couple weeks and even then I couldn't finish it. I said f it and watched the ending on Youtubez

Yeah, you'll slowly be able to cover weaknesses through fusion. There will be demons with resistances to certain elements and you should be able to transfer them to your fused demon. If you keep passing those resistances on, you could end up with monsters having as little resistances  to none to even immunities. Through this way, I got a few demons almost immune to all attacks, save a few.

So should I be picky with which demons I fuse with which, or should I just fuse as often as possible no matter what, and eventually the weaknesses will be phased out?

Hmmm, that is hard to say... I think with fusing, it's good to look at your options, see what they offer in stats and abilities, and pick the ones you think will help you the most. Though if you recruit multiple monsters, you could cover the demons you had to pass. As you gain access to stronger ones, they will naturally have better resistances, which will need less of the resistances you're getting from from other demons, so the demons will slowly smooth out.

Usually when I played, I wouldn't stick to demons very long, as they would learn all their other attacks they had and would have little else to do with them other than fuse. There are a few exceptions, as some demons will evolve into new monsters, so there's that option if you want to do that. Demons that can evolve will say so after a few level ups. I forgot the phrases, but they will tell you if they can change soon.

Also, I forgot, be sure to record the stats of any demons you have often, especially before fusion. You can buy those demons later if you want, with the stats and moves they had before fusion. This was you can use them again to fuse to make other demons, or just keep using that one if you like it.

So yeah, feel free to fuse a lot. I was picky because I really liked some of the demons I had and didn't want to lose them.

noname explained everything pretty well. Get demons who can strike weaknesses! Also you shouldn't be afraid of fusing demons since there is a demon compendium option. You can register demons there and summon them back (for a fee).

Okay, thanks! I'll keep that in mind!

Should I be using that a lot? It's pretty annoying recruiting a demon I've already recruited just because I've fused it away.

The compendium is useful to register demons that you liked/have a great combination of skills. Then you can summon them later to fuse them with other demons to make your new demon inherit those skills. Remember that everytime you fuse demons you can press b and cancel the fusion, and each time you chose to fuse them again the skill set of your new demon will be different. That way you can create demons with the skill sets you want.

But you shouldn't use it for common demons. Those can be recruited by talking to them! Just try talking with a lot of demons and you will start seeing a pattern, some of them react well to some answers. Soon you will get the hang of it and recruit any demon you want. There is always a random factor where the demon might leave or attack you anyway.